FIG. 1 shows radio resource control (RRC) service states 100 of a Third Generation Partnership Project (3GPP) wireless transmit/receive unit (WTRU) with an enhanced uplink (UL) in a Universal Mobile Telecommunications System (UMTS). The WTRU may operate in several states depending on user activity. The following states have been defined for UMTS Terrestrial Radio Access (UTRA) radio resource control (RRC) connected mode: IDLE 110, CELL_DCH 120, CELL_FACH 130, URA_PCH 140, and CELL_PCH 150. Other states that the WTRU may transition to include a general packet radio service (GPRS) packet transfer mode 160, or a global system for mobile communications (GSM) connected mode 170. RRC state transitions are controlled by the network using radio network controller (RNC) parameters. In general the WTRU does not decide to perform state transitions by itself.
Based on WTRU mobility and activity while in UTRA RRC connected mode (i.e., in the CELL_DCH, CELL_FACH, URA_PCH or CELL_PCH state), the UMTS Terrestrial Radio Access Network (UTRAN) may direct the WTRU to transition between the states CELL_PCH, URA_PCH, CELL_FACH, and CELL_DCH. Communication between the WTRU and the UTRAN, known as user plane communication, is only possible while in the CELL_FACH state or the CELL_DCH state.
In the CELL_DCH state, a dedicated physical channel is allocated to the WTRU in the UL and the downlink (DL). This corresponds to continuous transmission and continuous reception in the WTRU, which can be demanding on user power requirements. The WTRU is known on a cell level according to its current active set. An active set is a set of radio links simultaneously involved in a specific communication service between the WTRU and the UTRAN. The WTRU may use dedicated transport channels, shared transport channels, or a combination of these transport channels.
A WTRU is in the CELL_FACH state if it has been assigned to use the common channels (i.e., forward access channel (FACH), random access channel (RACH)). In the CELL_FACH state, no dedicated physical channel is allocated to the WTRU, which allows for better power consumption, at the expense of a lower UL and DL throughput. Downlink communication in the CELL_FACH state may be achieved through a shared transport channel (i.e., FACH) mapped to a shared common control physical channel (S-CCPCH). Downlink communication in the CELL_FACH state may also be achieved through a high speed downlink shared channel (HS-DSCH). The WTRU continuously monitors the FACH channel, carried over the S-CCPCH, or the HS-DSCH, in the DL. Uplink communication in the CELL_FACH state is achieved through a default common or shared transport channel (i.e., RACH) mapped to the RACH physical channel (PRACH), which the WTRU may use anytime according to the access procedure for that transport channel. The RACH channel is a contention based channel with a power ramp-up procedure to acquire the channel and to adjust transmit power. The position of the WTRU is known by the UTRAN on a cell level according to the cell where the WTRU last performed a cell update.
A characteristics of the CELL_FACH state includes being well-suited for applications requiring very low uplink throughput. Another characteristic of the CELL_FACH state includes being well-suited for signaling traffic, such as transmission of CELL UPDATE messages and URA UPDATE messages. Mobility in the CELL_FACH state is handled autonomously by the WTRU. The WTRU independently takes measurements and determines which cell to camp on. System information (SI), read from the broadcast channel (BCH), includes setup details for the uplink channel (RACH) and the downlink channels (FACH and HS-DSCH) to be used in the CELL_FACH state.
In the CELL_PCH state, no dedicated physical channel is allocated to the WTRU. The WTRU selects a paging channel (PCH), and uses discontinuous reception for monitoring the selected PCH via an associated page indicator channel (PICH). No UL activity is possible. The position of the WTRU is known by the UTRAN on a cell level according to the cell where the WTRU last performed a cell update in the CELL_FACH state.
In the URA_PCH state, no dedicated channel is allocated to the WTRU. The WTRU selects a PCH, and uses discontinuous reception for monitoring the selected PCH via an associated PICH. No UL activity is possible. The location of the WTRU is known on a UTRAN registration area (URA) level according to the URA assigned to the WTRU during the last URA update in the CELL_FACH state.
Recent 3GPP proposals have identified the possibility of using the enhanced dedicated channel (E-DCH) in the CELL_FACH state, also referred to as Enhanced RACH or E-RACH. The E-DCH was introduced in Release 6 of the 3GPP specifications to increase uplink throughput. The enhanced uplink operates on a request/grant principle. WTRUs send an indication of the requested capacity they require, while the network responds with grants to the requests. The grants are generated by a Node-B scheduler. Also, hybrid automatic repeat requests (HARQ) are used for physical layer transmissions. Further, new UL and DL channels were introduced in Release 6 to support the E-DCH. The new UL physical channels are the E-DCH dedicated physical control channel (E-DPCCH), which is used for control information, and the E-DCH dedicated physical data channel (E-DPDCH), which is used for user data. The new DL physical channels are the E-DCH absolute grant channel (E-AGCH) and E-DCH relative grant channel (E-RGCH), which are used for transmission of grants, and the E-DCH HARQ acknowledgement indicator channel (E-HICH), which is used for fast Layer 1 acknowledgement (ACK)/negative acknowledgement (NACK). The Node-B 220 may issue both absolute grants and relative grants. Grants are signaled in terms of a power ratio. Each WTRU maintains a serving grant, which it may convert to a payload size. For Release 6, WTRU mobility is handled by the network through soft handover and the concept of active sets.
In a pre-Release 8 high speed packet access (HSPA) system, the WTRU may be signaled to transition between different states. The transition between different states is defined, in pre-Release 8, for systems without E-RACH. However, with the introduction of the E-DCH in the CELL_FACH state and Idle mode, there are issues that occur when the WTRU is transitioning between states such as handling of available E-DCH resources, physical channel procedures, and allowing fast and smoother transitions between different states. Currently, for example, when the WTRU transitions from the CELL_DCH state to the CELL_FACH state, all the resources are released because the previous CELL_FACH state did not support E-DCH reception. However, this behavior may not be desirable when the WTRU moves from the CELL_DCH state to the CELL_FACH state where the cell supports E-DCH transmissions.
Accordingly, a method and apparatus for performing WTRU state transition with E-RACH in HSPA systems are desired.